The commuter plane that crashed near Buffalo on Thursday night slammed to the ground flat on its belly, with almost no forward momentum and facing opposite its intended route, seconds after two automatic warnings to the pilots that the plane was not moving fast enough to stay aloft, the National Transportation Safety Board said on Saturday.

The description indicates that the plane, a Bombardier Dash 8 Q400, suffered an aerodynamic stall, meaning the flow of air over the wings was either disrupted or too slow to sustain flight, but the reason why remains a mystery.

Icing, which the crew of the plane reported shortly before the crash, is one possible reason, but Steven Chealander, the safety board member assigned to the investigation and a retired airline captain, said the aircraft had a sophisticated ice protection system.

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The plane was equipped, he said, with pneumatic boots, which are a bit like tires, on the front edges of the wings, the tail and the vertical stabilizer, that inflate and contract twice a minute to break ice accumulations, as well as electrically heated propellers. The system gives an indication in the cockpit if any boot is not working, and so far, investigators have found no sign of such an indication, Mr. Chealander said.

“This Dash 8 is a workhorse airplane,” he said. “It’s not really susceptible to ice.”